Automatic variable coupler



Mfillf'fih 11, 1952 PRATT 2,589,@29

AUTOMATIC VARIABLE COUPLER Filed Jan. 18, 1950 I mg I.

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MOTOR mvencorz Harry G. @ratt, $09M 9 l hs Attorneg.

' form the desired output Patented Mar. 11, 1952 AUTOMATIC VARIABLE COUPLER- Harry G. Pratt, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application January 18, 1950, Serial No. 139,313

7 Claims. 1

This invention relates to coupling circuits for electrical signals and particularly to the type automatically controlling the degree of coupling.

It is often desirable in electrical energy transmission systems, especially of the type employing an unstable source whose output varies in intensity over a wide range, to extract a fixed amount of energy for calibration or control purposes. Several techniques are available for obtaining a fixed amount of energy from a source of variable intensity energy. This invention is directed particularly to the technique employing a calibrated reference signal for comparison with the extracted signal in order to obtain a measure of the amount of control necessary to achieve the fixed amount of extracted energy. One of the requirements of such a system is that control of the intensity of the extracted signal be possible over a wide range of fluctuations of the intensity of the signals at their source. It is also highly desirable that these be insured a fast and faithful response of the control circuit to fluctuations of the source.

It is an object of my invention to provide an improved arrangement for extracting a fixed amount of signal from a variable intensity signal source.

It is a further object of myinvention to provide a method and apparatus for extracting an adjustable predetermined amount of electrical energy from an energy source of fluctuating intensity.

It is a further object of my invention for providing an improved method and apparatus for comparing a normally variable electrical signal with a'fixed reference signal to obtain control signals useful in stabilizing said variable signals.

The novel features which I believe characteristic of my invention are set forth with particularity in the appended claims. My invention. however, both as to its organization and method of operation, together with further objects and advantages thereof, may'best be understood by reference to the following description taken. in connection with the accompanying drawings in which Fig. 1 shows my invention in block diagram form, Fig. la shows in graphical error signal-input signal difference characteristic achieved in accordance with my invention, and Fig. 2 is a circuit diagram disclosing a particular embodiment of my invention.

Fig. 1 shows a source of variable intensity energy as, for example, the radio frequency stage of a radio receiver coupled by means of a transpled through the mission line 2 to a load circuit 3 which may comprise the low frequency stages of a receiver. In order to derive a constant intensity signal from the output of source I as, for example, a detected radio frequency energy of substantially constant wattage and useful for controlling circuits I or 3 or for controlling an exterior mechanism, a portion of the output of source I is coupled by means of a variable coupling unit 4 to the output circuit 5, In order to maintain the input to circuit 5 constant over a wide range of energy intensity variation of the source I, a control circuit 6 is employed for adjusting the degree of coupling of circuit 4. Control circuit 6 comprises a detector 7 for detecting a portion of thevariable coupling output supplied to circuit 5 and for applying the detected output to a servo'control unit 8 which is also provided with a highly regulated reference signal from supply 9. The control unit 8 serves to compare the intensity of signals from sources I and 9 to derive an error signal indicative of the difference of intensity between these two signals. This error signal is coupled from the output of control unit 3 to a drive mechanism I 0 as, for example, a servo motor which is employed to control the degree of coupling of circuit 4. Circuit 8 is arranged such that variation of the intensity of the output of coupling 4 in either direction from a given intensity results in a control signal being applied to mechanism In to adjust the coupling circuit 4 in a proper direction to maintain a constant output thereof. When the signals supplied to control unit 8 from circuits 1 and 9 are substantially equal, however, the adjustment of the degree of coupling of circuit 4 is held fixed. The degree of control achieved with applicants arrangement is clearly shown by the steep null characteristic of Fig. 1a, where the abscissa refers to the difference between the reference and variable coupling output signals, and the ordinate refers to the intensity of output signal obtained for application to the circuit [6.

Briefly, an embodiment of applicants invention comprises the use of several groups of electron discharge devices having their electron discharge paths serially connected across a source of direct voltage. The devices are arranged into pairs, each comprising a device from each group. The variable intensity and reference signals are applied to the input circuits of respective devices of an initial pair of devices, and the amplifier versions of these signals are successively couremaining pairs of devices.

Certain of the pairs of devices are intercoupled to render the system more sensitive to input signal differences. The final pair of devices are arranged to have a signal difference indicator coupled between the cathode output circuits thereof. This arrangement is desirable to obtain a suitable indicator driving voltage permitting prompt and sensitive response to input signal differences.

Fig. 2 shows an embodiment of applicants invention in circuit diagram form comprising an arrangement for maintaining the amplitude of detected radio frequency voltage supplied over a coaxial transmission line H to a loadcircuit [2 from a radio frequency source of fluctuating voltage l3 constant over a wide range of fluctuations. An adjustable coupling condenser 14 is coupled between th coaxial transmission line I l and the input of the voltage control unit l5. In a preferred form, condenser I4 comprises a plate movable withrespect to the inner conductor of coaxial line II. By varying the coupling of the movable plate with respect to the inner conductor, the amount of voltage applied to control circuit l5 may be regulated. Detector circuit l6 detects the output of condenser I4 and couples it to an input electrode I1 of comparator circuit l8. Comparator circuit l8 comprises a pair of cathode coupled triodes l9 and 28 having a commonunbypassed cathode load resistor 2| and operating as a form of push-pull circuit. A source of adjustable amplitude reference voltage is available from the movable arm of potentiometer 22. Potentiometer 22 is coupled at one end to a source of negative potential and at the other end to ground. A voltage regulating tube 23 is coupled across the potentiometer 22 to maintain a substantially constant source of negative voltage from which a predetermined amount may be coupled by adjustment of potentiometer 22 to the input electrode 24 of tube 28. The plate voltage of tubes l9 and 28 is supplied from a positive voltage source, through the plate-cathode circuits of series connected tubes 25, 26 and 21, 28 respectively. Tubes 26 and 28 have their cathodes 29 and 38 tied together and coupled by means of a common current bypass resistor 3| to ground. This is necessary since in the particular embodiment disclosed tubes 28 and 28 draw considerably more plate current than do the voltage amplifiers I9 and 28. The cathode electrodes 29 and 38 of tubes 26 and 28 are also coupled through load resistors 32 and 33 to respective plate electrodes of tubes l9 and 28. Potentiometer 34 provided for adjusting the. relative amount of load resistance contained in tube circuits l9 and 28. The output of tube I9 is coupled to the input electrode 35 of tube 28 while the output of tube 28 is coupled to the input electrode 36 of tube 28. Cathodes 31 and 38 of tubes 25 and-21 are coupled by means of resistors to the plate electrodes of 28 and 28 respectively. The input electrodes 39 and 48 of tubes 25 and 21 are coupled to the output of tubes 25 and 28.

During operation of circuit 15, tubes i9, 28, 25, 28, 21 and 28 are conducting all the time. If the input signals toelectrodes I1 and 24 are equal, no voltage isdeveloped between cathodes 31 and 38. Potentiometer 34 is provided to adjust for the no voltage condition. If the negative signal from diode I6 applied'to electrode I1 is more. negative than thefnegative signal available at electrode 24, tube 28 will conduct more heavily than tubel9 thereby making the voltage available at electrode 35 more positive with respect to that at 36, hence lowering the positive voltage at electrode 38 with respect to electrode 48 whereby the voltage at cathode 31 is more negative than that at cathode 33. Across cathodes 31 and 38 is provided the field windings 4| of a permanent magnet D. C. motor 42 whose'output shaft is coupled by appropriate gearing to the movable plate of condenser 14. Thus it is seen that for a lowering in voltage of electrode l1 with respect to electrode 24, a negative voltage is available at cathode 31 with respect to cathode 38 thereby driving motor 42 in a direction to reduce the degree of coupling of condenser l4 and hence the amount of voltage available at electrode 11. The control voltage is developed across winding 4| until the voltages at electrodes I1 and 24 have onc again become substantially equal. By adjusting the movable arm of potentiometer 22, the voltage stabilization level may be varied in either direction.

Should the input voltage at electrode l1become less negative than the reference voltage at electrode 24, a lower positive voltage is devel oped at cathode 31 than at cathode 38 therebydriving the motor 42 in an opposite direction to control the degree of coupling of condenser 14 and hence increase the input voltage at electrode 11 to be substantially equal to the reference voltage. By providing a common cathod unbypassed load resistor for tubes 19 and 28, small voltage diiferences maybe detected and hence a finer degree of adjustment may be obtained since.

greater conduction of one section as, for example, tube 19 due to a more positive signal at electrode l1 relative to electrode 24 results in a biasing voltage developed across resistor 2lreducing the discharge current flow through tube 28. A

similar action on the part of tubes 26 and 28 further amplifies this signal difference-such that upon application to the winding 41 coupled across the outputs of devices 25 and 21,-sufiicient power will have been developed to adjust condenser 14 to equalize the signals applied to electrodes [1 and 24.

In the event of failure of source I3 such that.

no voltage is available in coaxial line H. control unit I5 would normally attempt to operate to raise the zero voltageavailable at electrode l1 to that of the reference level, thereby running the motor 42 needlessly. Hence, it is desirable to prevent operation of the control circuit l5 until a, given minimum level of signal voltage is available in transmission line I I. To this end.

a switching circuit 43 is provided for connecting the output of detector circuit [*8 bymeans of switch 44 to input electrode l1. Forv no signal.

on the transmission line H, switch 44 couples the input electrodes l1 and 24 together, thereby maintaining motor 42 fixed at its last position. Circuit 43 comprises a pair of triodes 45 and 46 having a common unbypassed cathode resistor 41 coupled to a source of negative potential. The input electrode 48 of tube 45 is suppliedwith available detected radio frequency energy from transmission line H by means of detector circuit" 58. The input electrode 5!, of tube 48 is coupled to an adjustable source of negative voltage avail-.

able at potentiometer 52. Between the output electrodes of tubes 45 and 46 is coupled the field coil 51 of the relay controlling the position of switch 44. The output electrodes of tubes 45 and 48 are coupled by load resistors to a source of positive potential. When no radio frequency energy is available in line H enough static or contact potential is developed across the output of 50 to provide negative bias at 48 balancing negative bias applied from 52 to 5|. Tubes 45 and 46 therefore conduct substantialy equallyl hence producing no voltage drop across winding 57 and thereby maintaining switch 44 in its lower position to prevent operation of motor 42. If the input signal at electrode 45 rises, as upon arrival of radio frequency energy, a resultant voltage is developed across winding 51 to raise switch 44 to its other position thereby coupling radio frequency voltage from circuit IE toinput electrode ll of the control circuit l8. Thus, it is seen the switching circuit functions such that for no radio frequency input voltage, a bias voltage is developedbalancing the reference voltage established by potentiometer 52 at electrode 51, and winding 51 is inoperative to raise 44 to couple input voltage to the control circuit [8. However, when radio frequency voltage is available, the balance is destroyed and relay winding 51 operates 44 to apply input voltage to circuit IS.

The arrangement set forth in Fig. 2 has been found to operate satisfactorily over a, wide range of input voltagev frequencies and intensity variations in providing a substantially constant output to very close tolerances for application to a load circuit 1 2.

While I have shown only certain preferred embodiments of my invention by way of illustration, many modifications will occur to those skilled in the art and I therefore wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. The combination, in a system for regulating the supply of signal voltage from a source to a load, a source of operating voltage, two pairs of electron discharge devices, each electron discharge device having an anode, a cathode, and a control electrode, the devices of each pair being connected in series across said source with a resistance in series between the anode of one device and the cathode of the other device, means to vary the potential of the control electrode of said other device with the anode potential of said one device of each pair, and means to supply to the control electrodes of said one device of each pair a voltage varying on said electrodes in opposite sense with variations in voltage on said load, and means responsive to the difference in potentials of the cathodes of said other devices of said pairs to control the voltage supplied to said load.

2. An arrangement for comparing the intensity of a variable signal with a reference signal comprising two groups of electron discharge devices, a source of unidirectional voltage, means for respectively coupling the electron discharge paths of the devices in each group in series across said source, each of said devices comprising an input and an output circuit, means for coupling said signals to respective input circuits of an initial device in each group, an indicator for indicating the intensity difference of said signals, means for coupling said indicator between an output circuit of the final devices in said groups, and means for coupling the remaining output circuit of each device to a respective remaining input circuit of a succeeding device in a respective series coupled group.

3. An arrangement according to claim 1 further comprising means for intercoupling a selected pair of devices, one from each group, to achieve push-pull operation.

l. An arrangement for comparing the intensity of a variable signal with a reference signal comprising two groups of electron discharge devices, a direct voltage source, means for respectively coupling the electron discharge paths of the devices in each group in series across said Source, each of said devices comprising an input circuit, an output circuit and a cathode electrode, said devices being arranged into afirst, second and third pair of devices, each comprising a device in each group, a common cathode impedance intercoupling said first and second pair offdevices, means supplying said signals to respective input circuits of said first pair of devices, means coupling the output circuits of said first and second pairs of devices to the input circuits of said second and third devices respectively, and an indicator for indicating the intensity difference of said signals coupled between the output circuits of said third pair of devices.

5. An-arrangement for comparing the intensity of a variable signal with a reference signal comprising two groups of electron discharge devices. a direct voltage source, means for respectively coupling the electron discharge paths of the devices in each group in series across said source, each of said devices comprising an input circuit, an output circuit, a cathode and an anode, said devices being arranged into a first, second and third pair of devices, each pair comprising a device in each group, a respective common cathode load impedance intercoupling the respective devices of said first and second pair of devices, means supplying said signals to respective input circuits of said first pair of devices, means coupling the output circuits of said first and second pair of devices to the input circuits of said second and third devices respectively, and an indicator for indicating the intensity difference of said signals coupled between the output circuits of said third pair of devices, the devices of said first and second pair of devices each comprising anode load impedances, said first and second load impedances also comprising the cathode load impedances of a respective device of said second and third pair of devices respectively.

6. A variable coupling arrangement for applying a predetermined amount of signal from a variable intensity signal source to a load comprising a source of reference signal, two groups of electron discharge devicesga direct voltage source, means for respectively coupling the electron discharge paths of the devices in each group in series across said source, each of said devices comprising an input circuit, an output circuit, and a cathode electrode, said devices being arranged into a first, second and third pair of devices each comprising a device in each group, separate means providing a push-pull intercoupling of the respective devices of said first and second pair of devices, means normally supplying said signals to respective input circuits of said first pair of devices, means coupling the output circuits of said first and second pair of devices to the input circuits of said second and third devices respectively, coupling means for applying signals from said source to said load, means coupled between the output circuits of said third pair of devices for controlling the degree of coupling of said coupling means, and means responsive to the intensity of variable signals falling below a minimum level for coupling said signals to a common input circuit of one of the devices of said first pair of devices.

7. An arrangement for controlling the degree of coupling of coupling means supplying signals from a variable intensity signal source comprising a reference signal source, two groups of electron discharge devices, a direct voltage source, means for respectively coupling the electron discharge paths of the devices in each group in series across said source, each of said devices comprising arr-input circuit, an output circuit, a cathode and an anode, said devices being arranged into a first, second and third pair of devices each comprisingfa device in each group, a respective common load impedance intercoupling the respective devicesof said first and second pair of devices in push pull, means supplying said signals to respective input circuits of said first pair of devices,- means coupling the output circuits of said first and second pair of devices to the input circuits of said second and third devices respectively, an indicator for indicating the intensity difierence of said signals coupled by the output circuits of said third pair of devices, the devices of said first and second pair of devices each comprising anode load impedances, said first and second load impedances also comprising the cathode load impedances of a respective device of said second and third pair of devices respectively, means coupled between the cathodes of said third pair of devices for controlling the degree of coupling of said coupling means.

HARRY G. PRATT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,203,468 Martin June 4, 1940 2,340,175 Chance Jan. 25, 1944 2,457,792 Wild et a1. Dec. 28, 1948 2,467,335 Rath Apr. 12'; 1949 FOREIGN PATENTS Number Country Date 620,028 Great Britain Mar. 18, 1949 

